The present invention relates to a cable protection spring for protecting a cable from mechanical damage and a method for fixing the cable protection spring to a structure.
In the case of disposing an electric cable in a structure such as a mechanical device or a casing, it is known to pass the electric cable within and through a coil spring in order to protect the electric cable from mechanical damage caused by, for example, stress due to strong bending, rub due to contact with a rough surface, shear due to contact with a sharp portion. A coil spring used for such a use is generally called a cable protection spring. In particular, in the case of disposing a power cable, a signal line or a pipe for a pneumatic device within the arm of an articulated robot, the cable etc. moves relatively within the arm in accordance with the movement of the arm. Thus, the cable protection spring for protecting the cable etc. from the damage caused by being rubbed is indispensable.
The conventional cable protection spring has such a simple shape that the diameter thereof is constant along its entire length, and so a saddle having an xcexa9-shaped section is employed in the case of fixing the cable protection spring to a structure etc.
FIG. 5 is diagrams for explaining a state where the conventional cable protection spring is fixed to a structure etc, in which (a) is a plan view and (b) is a side view seen along a line A-Axe2x80x2 in (a). In the figures, numeral 1 depicts a cable protection spring which is a coil spring formed by winding a steel wire with a fine interval. The diameter of the cable protection spring 1 is constant along its entire length. Numeral 2 depicts a structure, that is, to be more concrete, the arm of an industrial robot etc. Numeral 3 depicts a saddle which is an ironmongery goods formed by bending a rectangular steel plate into an xcexa9-shape. The saddles 3 are attached on the structure 2 so as to cross over the cable protection spring 1 in a manner that the cable protection spring 1 is fastened or gripped by the xcexa9-shaped sectional inner side of the saddle and fixed to the structure 2 by means of screws 4.
However, such a conventional cable protection spring requires a dedicated ironmongery goods such as a saddle for fixing the spring to a structure and further requires a tool such as a screwdriver or a wrench in order to fix the ironmongery goods. Thus, since the number of parts and the number of assembling processes increase, there arises a problem that a cost of the spring increases.
Further, there is another problem that skilled technique is required to fix the saddle. That is, if the saddle is fixed in a state that the spring is squeezed, that is, the spring is pushed down and deformed in an elliptic shape in its section, the spring will come out of the saddle easily when the robot moves and a tension acts on the spring. Thus, it is required to fix the saddle while paying attention so as not to deform the spring.
Accordingly, an object of the present invention is to provide a cable protection spring capable of being attached and fixed through one-touch operation without requiring an ironmongery goods or a tool for fixing. Further, an object of the present invention is to provide a method for attaching and fixing a cable protection spring through one-touch operation.
In order to attain the aforesaid object, the invention claimed in claim 2 is a cable protection spring which a wiring cable is passed within and through a coil spring to protect the wiring cable from mechanical damage. The cable protection spring is characterized in that the coil spring is provided with a portion having a diameter larger than a diameter of remaining portion thereof, and a winding interval of the large diameter portion of the coil spring is made larger than a winding interval of the remaining portion of the coil spring. Further, the invention claimed in claim 4 is a method for fixing a cable protection spring wherein the coil spring is provided with a portion having a diameter larger than a diameter of remaining portion thereof, the structure is provided with a groove having an inlet and an outlet with a small width and a center portion with a large width, the large diameter portion of the coil spring is compressed and pushed into the center portion of the groove thereby to fix the coil spring within the groove by a force acting at the center portion of the groove which is generated at the large diameter portion of the coil spring by trying to restore to its original length. The invention claimed in claim 3 is a method for fixing a cable protection spring wherein the coil spring is provided with a portion having a diameter smaller than a diameter of remaining portion thereof, and the structure is provided with a groove having an inlet and an outlet with a large width and a center portion with a small width, the small diameter portion of the coil spring is expanded and pushed into the center portion of the groove thereby to fix the coil spring within the groove by a force acting at the center portion of the groove which is generated at the small diameter portion of the coil spring by trying to restore to its original length.